This study is exploring the significance of serum creatine phosphokinase (CPK) increases in acutely psychotic patients. Serum CPK levels are elevated during the first days of a psychotic exacerbation in 50-60% of psychotic patients. The origin of the CPK appears to be skeletal muscle but may be brain. The patients with increased serum CPK levels appear to have more florid symptomatology and also have higher mean serum CPK levels in non-psychotic periods. Sleep disturbance and minor trauma may contribute to the increased serum CPK levels but it is possible that the increases are due to central nervous system dysfunction which might lead to alterations in muscle cell membrane properties. First-degree relatives of psychotic patients tend to have increased levels of pyruvate kinase. The proposed study will attempt to replicate and extend these findings. Phencyclidine, a psychotomimetic, plus restraint stress, can markedly increase serum CPK activity in rats. The proposed study will explore the mechanism of this increase. The role of serotonin in inducing muscle pathology in rats will be studied. The effects of the psychotomimetic drug harmaline on plasma CPK levels will be studied.